Wildly fluctuating battery voltage

[Wilbur's son]

Hey guys,

Battery/charging system questions here. I've had my BD for a year now and the battery voltage gauge always showed between 14.8 and 15.2. Until this week. My drive home from work (15 miles) Monday was 14.8 voltage. Tuesday 14.6. Wednesday 14.4. Thursday 13.8. Then today was all over the place. From 14.6 down to 12.8. Would bump up when decelerating/downshifting, but then drop again. Has anyone experienced this? Normal range of activity or bad abnormal? Causing damage? Is it a battery problem or a voltage regulator problem? Does anyone know at what number does the Bronco "code out" and shutdown?

Thanks Mark

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[HBTFD]

My BD has always varied from 13-15.

 

[Wilbur's son]

My BD has always varied from 13-15.

Thanks. Usually I only drive my BD on weekends. My '01 Ranger broke a rear brake shoe then jammed in the drum. So forced into daily driving. Just hadn't seen voltage activity like this before.

 

[Billnchristy]

Yeah ours is crazy too.

 

[Lifeliberty]

From what I know, it says battery voltage on your meter, but what it actually measures is the alternator output. It's sort of misleading. And this can change depending on how much your battery needs, the alternator adjusts higher if your battery needs it.

I think anywhere between 12-16 is fine.
Below 10 and something will need changed out

If anyone knows more feel free to discuss.

 

[Wilbur's son]

From what I know, it says battery voltage on your meter, but what it actually measures is the alternator output. And this can change depending on how much your battery needs, the alternator adjusts higher if your battery needs it.

If anyone knows more feel free to discuss.

Thanks, I hadn't thought about it that way. Just from a draw on the battery perspective.

 

[RagnarKon]

Completely normal.

Ford has a battery management controller in these vehicles these days, and because it is running an AGM battery rather than the traditional lead acid the voltage can jump around and spike higher than lead-acid batteries.

Charging voltage in lead-acid is around 14.4 volts maximum, and your typical alternator made for a lead-acid will run between 13.8 and 14.4 volts when it is charging the battery. AGM battery charging voltage can be as high as 15.3 volts. And theoretically (in cold weather below freezing) you can feed it even higher voltage than that.

 

[Wilbur's son]

Completely normal.

Ford has a battery management controller in these vehicles these days, and because it is running an AGM battery rather than the traditional lead acid the voltage can jump around and spike higher than lead-acid batteries.

Charging voltage in lead-acid is around 14.4 volts maximum, and your typical alternator made for a lead-acid will run between 13.8 and 14.4 volts when it is charging the battery. AGM battery charging voltage can be as high as 15.3 volts. And theoretically (in cold weather below freezing) you can feed it even higher voltage than that.

Thanks for the additional details. I was sweating a service call (if I could even get in) before a July 4th trip to Colorado. As a side note, I have been concerned about the trapped engine heat and its effect on the battery, so I pop the hood when in the garage every evening to help cool things off. Don't know if this makes any difference or not.

 

[BostonSasquatch]

If something is drawing power and draining the battery -- an interior or accessory light, for example? -- will the battery shut down supplying current to conserve its charge?

 

[Wilbur's son]

If something is drawing power and draining the battery -- an interior or accessory light, for example? -- will the battery shut down supplying current to conserve its charge?

I think those items "time out" and turn off. I don't know if the AUX switches are the same or have to be manually switched off. But if you have a closed circuit somewhere else, the draw continues. Someone correct me if I am wrong.

 

[RustysBronco]

It sounds like it's alternating. Seems like that's within the design specifications of an alternator to me.

 

[Ducati1098]

Per the WSM:

The PCM controlled Smart Charge charging system determines the optimal voltage setpoint for the charging system and communicates this information to the voltage regulator. The Smart Charge charging system is designed to set a DTC when a charging system fault is present. All of the DTC can set continuous faults, but not all DTC 's set as on-demand faults.

The smart regenerative charge system primary strategy is stored in the BCM . The BCM receives information relating to the battery condition from the battery monitoring sensor via a LIN . The BCM calculates and sends the set value needed for the generator charging voltage via the HS-CAN to the PCM . The PCM then adjusts the value received (if necessary) and sends it to the generator via a different LIN . The charging voltage is adjusted depending on various parameters, such as the current level of engine efficiency. The smallest possible set value for the generator voltage is 12.2 volts, while the maximum charging voltage can be anywhere between 14.5 and 14.9 volts. However, when the battery is in a refresh phase, the voltage may occasionally reach up to 15.2 volts. These refresh phases are required when the battery charge status is 80% over long periods of time, which increases the risk of sulfation in the battery cells.

The PCM simultaneously controls and monitors generator output. When the current consumption is high or the battery is discharged, the PCM raises engine speed as needed to increase generator output. The generator charges the battery and at the same time supplies power for all electrical loads. The battery is more effectively charged with a higher voltage when the battery is cold and a lower voltage when the battery is warm.

 

[Wilbur's son]

Per the WSM:

The PCM controlled Smart Charge charging system determines the optimal voltage setpoint for the charging system and communicates this information to the voltage regulator. The Smart Charge charging system is designed to set a DTC when a charging system fault is present. All of the DTC can set continuous faults, but not all DTC 's set as on-demand faults.

The smart regenerative charge system primary strategy is stored in the BCM . The BCM receives information relating to the battery condition from the battery monitoring sensor via a LIN . The BCM calculates and sends the set value needed for the generator charging voltage via the HS-CAN to the PCM . The PCM then adjusts the value received (if necessary) and sends it to the generator via a different LIN . The charging voltage is adjusted depending on various parameters, such as the current level of engine efficiency. The smallest possible set value for the generator voltage is 12.2 volts, while the maximum charging voltage can be anywhere between 14.5 and 14.9 volts. However, when the battery is in a refresh phase, the voltage may occasionally reach up to 15.2 volts. These refresh phases are required when the battery charge status is 80% over long periods of time, which increases the risk of sulfation in the battery cells.

The PCM simultaneously controls and monitors generator output. When the current consumption is high or the battery is discharged, the PCM raises engine speed as needed to increase generator output. The generator charges the battery and at the same time supplies power for all electrical loads. The battery is more effectively charged with a higher voltage when the battery is cold and a lower voltage when the battery is warm.

Thanks. Wow. Great info. Not sure it is all sinking in tonight. Will have to reread tomorrow morning. The most import detail I gleaned tonight is that I haven't been driving my BD enough if the battery was always in refresh phase. It was constantly reading 15.2 for months.

 

[2023bronco]

Glad I found this thread.

I just noticed the wild fluctuation today. I nearly pulled over to check the ground because I was thinking it was happening when I hit bumps, but those just happened to coincide with lifting off the throttle, LOL. The gauge simply changes depending on load.

Confounding to me like the oil temperature gauge instead of an oil pressure gauge!

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